Spinal stenosis is a degenerative condition of the spine that afflicts primarily the elderly population. Patients with lumbar spinal stenosis suffer from severe radiating pain, which limits their ability to ambulate and can cause weakness and numbness in the legs and in severe cases, loss of bowel and bladder control may occur. It is the development of hypertrophic bone spurs off the facet joints, protrusions of the disc annulus, as well as hypertrophy of the ligamentum flavum that combine to narrow the space available for the nerves in the spinal canal.
The standard surgical procedure to treat lumbar spinal stenosis is known as the lumbar laminectomy and foraminotomy. During this procedure, the surgeon removes the spinous processes, the interspinous ligaments and the central portion of the spinal lamina to gain a line of sight into the lateral recess and into the foramen so that the nerve compression can be relieved in these areas. The current standard tools for performing this procedure are the Kerrison punch and angled curettes and in severe instances, osteotomes. To remove the offending bone using these instruments, a surgeon places the instrument into the interval between the compressing bone and the underlying nerve that is being compressed and the bone is then removed from the dorsal aspect of the nerve where it is impinged, thereby relieving compression exerted on the spinal nerve. In situations where the compression on the nerve is not very severe, one can safely insert the Kerrison footplate or the curette into the interval between the nerve root and the surrounding bone to perform the necessary bone removal.
However, when there is a severe amount of compression at the neural foramen or the lateral recess, the interval between the nerve root and the encroaching bone may not be sufficient to safely conduct the neural decompression using the conventional tools, such as a Kerrison punch or a curette. Insertion of a Kerrison footplate or a curette into a severely stenotic interval may cause compressive injury to an already compressed nerve root. In these situations, the only conventionally available method of successfully decompressing the neural compression, especially in the foramen, has been to pass a small curved osteotome in the plane that is superior to the nerve root and osteotomize the bone that is encroaching on the nerve root from above. This maneuver, however, poses risk to the nerve root because there is a possibility that the osteotome will slip or advance too deep, thereby damaging the exiting nerve. Thus, there is a need for an improved instrument that would allow a safer, more controlled method of foraminal lateral recess decompression that minimizes risks to the nerve roots, especially in severely stenotic situations.
Additionally, the need to remove the interspinous ligament, the spinous processes and the central portion of the lamina in open lumbar laminectomy is only to allow the surgeon to have a line of sight into the lateral recess and foramen to remove pressure on the compressed nerve. In surgery, the surgeon works from the opposite side of the table to get the appropriate line of sight and angle of attack at the encroaching bone and soft tissue in the lateral recess in the foramen. Working from the contralateral side of the table is necessary in order to be able to undercut the facet joints and thereby preserve spinal stability with these procedures. This line of attack is necessary because of the shape of the current standard instruments, such as a Kerrison punch, curette or osteotome, and the necessary vector of applied force that is required using those instruments. There is therefore an additional need for an instrument that would allow for ipsilateral decompression of the lateral recess and the foramen. This instrument would need to allow for undercutting of the facet joints and removal of compressive bone and soft tissue in the lateral recess and the foramen on the ipsilateral side of the patient (decompression on the same side of the table as opposed to working across the spinal canal from the contralateral side of the table). Such an instrument would also allow for the application of minimally invasive techniques to perform lumbar decompressions and would allow for the maximal preservation of bone and ligaments thereby preserving spinal stability.
One tool that is available to a spine surgeon to remove bone, in a controlled fashion, is a high speed burr. The burr is used from the dorsal surface of the bone heading towards the neural elements and the bone is thinned down until it is wafer thin and can be picked away with curettes. If one is too aggressive with the burr, then neural injury can occur by penetrating the dura or wrapping the neural elements in the burr bit. Because the risk of catching the neural elements with the conventional high speed burr bit is too high, the use of conventional high speed burrs to perform the lateral recess and foraminal decompression has not been practicable. Thus, an improved novel high speed burr for removing bone in such tight spaces is desired.